1. Technical Field
This invention relates to a photoelectric conversion element and a solid-state imaging device.
2. Related Art
Research and development have been directed toward organic photoelectric conversion elements using an organic compound. An organic photoelectric conversion element includes a stack of a photoelectric conversion layer that absorbs light to generate charge, a pair of electrodes having the photoelectric conversion layer therebetween, and a plurality of functional layers such as a charge blocking layer that prevents charge injection from the electrode(s) into the photoelectric conversion layer as described, e.g., in JP-A-2007-88033. Fabricating an imaging device using the organic photoelectric conversion elements includes a color filter forming step, a wire bonding step, and the like steps that involve heating as well as the steps of forming the photoelectric conversion layer, electrodes, and charge blocking layer. Because the photoelectric conversion element or the resulting imaging device is subjected to high temperatures of 200° C. or higher during these heating steps, the organic photoelectric conversion element containing a thermally unstable organic compound is required to undergo no deterioration of performance due to heat treatment at 200° C. or higher.
JP-A-2008-288253A proposes a method of fabricating an organic photoelectric conversion device, which method includes providing an anti-deterioration layer on a photoelectric conversion layer followed by heat treatment (annealing) and removing the anti-deterioration layer after the heat treatment. JP-A-2008-288253 states that the performance of the photoelectric conversion layer is improved by annealing without causing deterioration of the performance of the device. The method, however, does not provide a solution to the problem that the performance of the organic photoelectric conversion device is deteriorated by the high temperature applied in the formation of color filters because the anti-deterioration layer is removed after the annealing.
The deterioration of performance of an organic photoelectric conversion device by the high temperatures of 200° C. or higher could be avoided by making the organic layer of the device of a material having a glass transition temperature (hereinafter “Tg”) of 200° C. or higher. Nevertheless, this approach, although it prevents the performance deterioration by heat, narrows the range of choice for the organic layer material, making it difficult to attain high performance properties.